When used for park assist, an ultrasonic system defines a trajectory for the vehicle, and determines a target parking slot based on the sensor readings. The parking slot can be for perpendicular or parallel parking slots, as examples. However, an error state can occur when scanning for a parking slot, when instead of reading reflected ultrasonic waves the sensor picks up emissions or waves emitted from other vehicles or sources. An error state can also occur when signals are reflected from other vehicles.